Embodiments of the invention relate to a concept for determining a magnetization direction of an indicator magnet. Further embodiments of the invention relate to automatic detection of the magnetization direction in position measurement systems on a magnetic basis.
In the field of linear position measurement system on a magnetic basis, it has long been common to use Hall sensors in connection with moving permanent magnets to monitor single axis linear movements. In principle, such systems are structured as shown in FIG. 10. There is a fixed sensor 10 across which a permanent magnet 12 moves in a linear manner. The sensor 10 measures respective magnetic field values and provides these values to an evaluation unit calculating a current position of a magnet 12 therefrom. In the coordinate system shown in FIG. 10, the X axis is essentially parallel to the linear axis of movement of the permanent magnet 12. Further, X axis and Z axis are in the plane of the drawing, while the Y axis is perpendicular to the plane of the drawing.
According to the known technology, there are different evaluation approaches for determining the position of a moving magnet with Hall sensors.
The most simple form of a procedure for position determination known in the technology uses the linear range 20 of the Z components 22 of the magnetic field, as shown exemplarily in FIG. 11. For the illustrated example, this is possible in the range of −0.005 m to +0.005 m (=+/−5 mm). Significant non-linearities occur at the boundaries, such that linearization has to be used already for this relatively small measurement range.
This type of evaluation is relatively easy to implement but has great disadvantages during application. On the one hand, magnet temperature and, for example, production-induced scattering of the magnetization have a direct influence on the measurement accuracy, since the position value is directly derived from the absolute value of a magnetic field component. On the other hand, the useable travel range of the permanent magnet with respect to the sensor in relation to the area where measurable fields (i.e. fields that are significantly larger than the earth's magnetic field of approximately 50 μT) of the magnet exist, is relatively small. Thus, with this method, neither the detection range of the sensor nor the magnetic field components provided by the permanent magnet are utilized fully and additionally, a position signal depending on the temperature of the permanent magnet results.
In a further procedure known in the conventional technology according to DE 19836599 A1, in order to be independent of the temperature of the magnet, a method is used that uses the ratio of the two magnetic field components Bx 30 and Bz 22 and, for example, its arctan calculation for position determination (see FIG. 12). Since the position is determined from the ratio of two field components, this method is independent of the temperature, both of the sensor chip and the magnet. Further, the usable travel range is larger than in the method described above.
However, there is the general problem that also in this method according to FIG. 12, the travel range is not limited by the height of the measured field components but by the evaluation method. Thus, also in this method, the theoretically possible travel range between sensor and permanent magnet is also not utilized fully.